1. Field of the Invention
The present invention relates to a new method of manufacturing high pressure fuel injection pipe materials to be used mostly for fuel feeding pipes for Diesel internal combustion engines and is made with a view to greatly improving the smoothness (coarseness) of the inside surface of the hole of an injection pipe and to improving the true circularity of the hole shape and the uniformity of the hole diameter.
2. Description of the Prior Art
In conventionally manufacturing a high pressure fuel injection pipe material, a carbon steel pipe obtained by hot-drawing is used to make a desired pipe by the repetition of annealing and drawing it. However, by the influence of a black skin layer or hair crack layer present on the inside surface of the hole of the pipe material, the inside surface of the hole of the pipe lacks in the smoothness, the hole shape lacks in the true circularity and the uniformity of the hole diameter and no satisfactory pipe is obtained. Therefore, the chemical treatment of the inside surface is attempted before annealing and drawing it. However, the precision required of the product is so strict that, even by such treatment, no satisfactory one is obtained today. (As the prior arts there are, for example, Japanese Patent Laid-Open Prints No. 93569/48 and No. 756/52.)